show Abstracthide AbstractWhile microbiome and pregnancy are known to alter drug disposition, the interplay of the two physiological factors to impact expression and/or activity of drug processing genes (DPGs) has yet to be elucidated. This study aimed to investigate the effects of microbiome on host hepatic DPGs during pregnancy using conventional (CV) and germ-free (GF) mice. Four groups of female mice were used, namely CV non-pregnant (CVNP), GF non-pregnant (GFNP), CV pregnant (CVP), and GF pregnant (GFP) mice. Pregnant mice examined were on gestation day 15. Transcriptomic and targeted proteomics of hepatic DPGs were profiled using a multi-omics approach. Plasma bile acid and steroid hormone levels were quantified using LC-MS/MS. Cyp3a activities were measured by mouse liver microsome incubations. While the overall trend in pregnancy-induced changes in the expression or activity of hepatic DPGs in CV and GF mice was similar, significant differences in the magnitude of changes were observed. For certain genes, we noticed opposite effects of pregnancy on mRNA and protein expression of DPGs in both CV and GF mice. For instance, the mRNA levels of Cyp3a11, the murine homolog of human CYP3A4, were decreased by 1.7-fold and 3.3-fold by pregnancy in CV and GF mice, respectively. However, the protein levels of Cyp3a11 were increased similarly ~2-fold by pregnancy in both CV and GF mice. Yet, microsome incubations revealed a marked induction of Cyp3a activity by pregnancy that was >5-fold greater in CV mice than that in GF mice. Plasma bile acid and steroid hormone levels were also significantly altered by microbiome and pregnancy, respectively, which may contribute to the differential effects of pregnancy in CV and GF mice. This is the first study to show that microbiome can alter hepatic DPGs in pregnancy. Overall design: Four groups of female mice were used, namely conventional non-pregnant (CVNP), germ-free non-pregnant (GFNP), conventional pregnant (CVP), and germ-free pregnant (GFP) C57BL/6 mice. Liver tissues from 6 CVNP, 5 CVP, 6 GFNP, and 5 GFP mice were collected.